<?php

//----------------------------------------------------------
// The combination of array_shift/array_unshift 
// greatly simplified a function I created for 
// generating relative paths. Before I found them 
// the algorithm was really squirrely, with multiple 
// if tests, length calculations, nested loops, etc. 
// Great functions.
//----------------------------------------------------------

function create_relative_path($inSourcePath, $inRefPath)
{
    // break strings at slashes
    $s_parts            = explode('/', $inSourcePath);
    $r_parts            = explode('/', $inRefPath);
    
    // delete items up to the first non-equal part
    while ($s_parts[0] === $r_parts[0])
    {
        array_shift($s_parts);
        array_shift($r_parts);
    }
    
    // add wild card to r_parts for each remaining 
    // item of s_parts
    while ($s_parts[0])
    {
        array_unshift($r_parts, '..');
        array_shift($s_parts);
    }
    
    return implode('/', $r_parts);
}

//----------------------------------------------------------
// Example:
//     Given a source path $sp generates the relative 
//     location of $rp. $sp could be assigned using 
//     $_SERVER['PHP_SELF'] but it's hardcoded for 
//     the example.
//----------------------------------------------------------
$sp = '/WebServer/Documents/MyBigProject/php/project_script.php';
$rp = '/WebServer/Documents/MyLibraries/lib_script.php';

// plugging them into the function
$rel_path = create_relative_path($sp, $rp);

// yeilds
'../../../MyLibraries/lib_script.php'

// and it could be used like
include_once(create_relative_path($_SERVER['PHP_SELF'], $rp));